1. Field of the Invention
The present invention relates to a liquid crystal display device and a method for producing a liquid crystal display device. More particularly, the present invention relates to a liquid crystal display device comprising the display component of an information equipment terminal, television or home appliance product, and a method of producing the liquid crystal display device.
2. Description of Related Art
In recent years, as information equipment has become more compact and lightweight, display devices to be mounted on such equipment have been sought that consume less power. Liquid crystal display devices, by means of the TN mode, are utilized as reflective displays in small display capacity equipment. Liquid crystal display devices, by means of the FTN mode, are utilized in mid-range display capacity equipment. Furthermore, uses wherein an information input apparatus, such as a tablet or the like, is included on the reflective-type display are also expanding, and brightness and good visibility are required in reflective-type liquid crystal display devices.
However, because TN-format and FTN-format liquid crystal display devices that use conventional polarizing plates have low light utilizing efficiency, the problem arises that these displays become dark when made reflective. Moreover, an extremely dark display results when an information input apparatus, such as a tablet or the like, is included. In addition, because a reflective plate is placed over the polarizing plate on the back surface of the substrate, positioned on the back side of the device, in order to make a reflective model with TN format or FTN format, double images occur in the display, small characters are unclear, and there are problems with visibility.
On the other hand, bright reflective-type displays that do not use polarizing plates have come to be developed recently. For example, a liquid crystal display device that uses a polymer dispersion liquid crystal in which liquid crystal and polymer are mutually dispersed, and that performs control so that the display is transparent when an electric field is applied and the light is scattered when no electric field is applied has been disclosed (Japanese Laid-Open Patent Publication Sho 58-501631). Liquid crystal display devices that perform control so that the light is scattered when an electric field is applied and the display is transparent or light is absorbed when no electric field is applied have also been disclosed (European Patent Application EPO 488116A2, Japanese Laid-Open Patent Publication Hei 4-227684, Japanese Laid-Open Patent Publication Hei 5-119302).
In particular, in the polymer dispersion-type liquid crystal display device using a polymer dispersion liquid crystal disclosed in European Patent Application EPO 488116A2, in which the liquid crystal and polymer are mutually orientation dispersed, it is possible to also use the electrodes as light reflecting surfaces because no polarizing plate is used. In this case, visibility, high precision and brightness, which cannot be achieved in TN and FTN modes that require polarizing plates, are obtained, and it is possible to obtain a reflective display with superior display quality.
However, the conventional art that has been disclosed with regard to polymer dispersion type liquid crystal display devices use polymer dispersion liquid crystal in which the liquid crystal and polymer are mutually orientation dispersed. Although it is possible to resolve the problems of a liquid crystal display device that uses a polarizing plate, it is necessary for the liquid crystal to be twisted by not less than 360.degree. in order to obtain sufficient scattering characteristics and to secure brightness. As a result, the problem arises that the driving voltage becomes high.
For example, large capacity displays are possible by forming active devices such as TFT (thin film transistor) or MIM (metal-insulator-metal) devices at each pixel and providing electric signal control at each pixel. However, because the driving voltage of the polymer dispersion liquid crystal is high, it is difficult to drive the liquid crystal so that the liquid crystal responds adequately from the standpoint of the voltage resistance of active devices. The problems also arise that the contrast ratio tends to fall and driving drivers are necessary that can withstand high voltages.
In addition, because of the orientation dispersion structure, the problem arises that there is directivity in the scattering. Directivity is when the light scattering efficiency changes based on the direction of the external incident light. For example, the brightness changes as the panel is rotated, and the problem then arises that the visibility is easily influenced by the usage environment. To the extent that the twisting of the liquid crystal is small, the directivity is larger. Accordingly, the twisting of the liquid crystal should be made larger in order to resolve this problem, but when this is done, the driving voltage becomes large. Consequently, making the twisting larger is impossible from the standpoint of the driving voltage.
Furthermore, when large quantities of a chiral agent are added in order to create a large twisting force, the problem arises that hysteresis is created in the electro-optical properties.
The present invention was made in order to solve these types of problems, and its purpose is to provide a liquid crystal display device, through controlling to a new orientation state a liquid crystal that is mutually orientation-dispersed with a polymer. The liquid crystal display device can be operated at low voltage, is bright, has a high contrast ratio, has improved scatter directivity, and has visibility that has only low dependence on the usage environment and which has superior portability. The present invention is also directed to the method of producing such a liquid crystal display device.